1. Field of the Invention
This invention relates to phase detectors for mark/space modulated signals.
2. Description of the Prior Art
Such phase detectors are advantageously used in phase-lock loops of static single-phase or multi-phase electricity meters which operate in accordance with the mark/space modulation method and which serve for the measurement of reactive energy and therefore, as is known, include a 90.degree. phase shifter. The phase-lock loop regulates the phase of its output signal u.sub..phi. in such a way that the difference .phi. between that phase and the phase of its input signal u.sub.o is equal to 90.degree. so that the phase-lock loop represents an active 90.degree. phase shifter.
The construction and mode of operation of an electricity meter which operates on the basis of the mark/space amplitude modulation method is known, for example, from U.S. Pat. No. 3,602,843.
A 90.degree. phase-lock loop which comprises digital components and which is used in an electricity meter for reactive energy, and the mode of operation thereof, are known from U.S. Pat. No. 4,594,547. The digital components referred to therein may be at least partially replaced by analog components, thus in particular a delay member which operates as a phase shifter can be replaced by an analog-type phase shifter as shown in FIG. 8 of the accompanying drawings, and an accumulator which operates as an integrator can be replaced by an analog integrator. The electricity meter for reactive energy is then of the structure shown in FIG. 1 of the accompanying drawings.